1. Field of the Invention
The present invention relates generally to the production of curved glass sheets, and more particularly to an improved method of and apparatus for bending glass sheets to a relatively deep curvature.
2. Description of the Prior Art
Curved or bent glass sheets are commonly employed as glazing closures for automobiles and the like. The configuration of the glazing closure, that is, the size, shape and curvature, is dictated by the opening in which the unit is to be installed and the overall design of the automotive vehicle. As will be readily apparent, with the many different designs and body styles of automotive vehicles in production at any one time, it is necessary to produce many different styles of glazing closures. The curvature, or bend, of the glazing closures can vary from a simple, shallow curvature to a relatively deep, compound curvature.
It has recently been proposed to use glass to form the satellite dishes employed in the telecommunication industry for receiving and focussing broadcast microwave radiation. The dish can be produced from a sheet of clear or colored glass that is provided with an appropriate metal oxide coating which reflects microwave radiation. The glass sheet may be bent to the necessary dish form on a conventional press bending apparatus utilized to produce the automotive glazing closures and may be either tempered or annealed, as desired.
In a preferred method of producing the automotive glazing closures and satellite dishes in the large quantities required for efficient production, flat sheets of glass are typically heated to their softening temperature in a suitable heat treating furnace. The softened sheets are thereafter pressed to the desired curvature between complemental shaping surfaces. The curved or bent sheets are then either rapidly chilled so as to develop a desired degree of temper or are gradually cooled in a controlled manner within the annealing range of glass. These operations are generally carried out in successive steps while the sheets of glass are being substantially continuously advanced by conveyor along a horizontal path including, in succession, a heating area, a bending area, and a tempering or annealing area wherein the residual heat in the sheet following bending can be utilized for the final heat treating or tempering operation.
The aforementioned complemental shaping surfaces are formed on opposed press members, each mounted on a supporting platen. The press members and their respective platens are normally located one above and one below the horizontal path of movement of the advancing glass sheets to receive the sheets therebetween, and are relatively movable toward and away from each other for pressing the sheets to the desired shape. A hydraulic cylinder is generally employed for raising the lower platen and press member upwardly to engage and lift a heated glass sheet from the conveyor system, out of the horizontal path, and press it against the shaping surface of the opposed or upper press member. The lower platen is then lowered to deposit the bent sheet upon the conveyor system for advancement into and through an adjacent tempering or annealing section. The conveyer system is typically comprised of a plurality of longitudinally spaced rolls which provide suitable support for the heat softened glass sheet as it is conveyed through the bending area. Alternatively, the upper press member may be of the vacuum-type to support the sheet after bending as the lower press member is retracted and a carrier ring is moved into position to receive the sheet and advance it into the appropriate cooling section.
As heretofore mentioned, the upper and lower press members are mounted on their respective platens and are relatively movable toward and away from each other to bend the sheets to the desired shape. A hydraulic cylinder is generally employed for raising and lowering the lower platen during the pressing cycle, while a screw jack system or the like, is utilized for adjusting the elevation of the upper platen and associated press member relative to the lower press member. The upper press member generally is set at a predetermined elevation for the particular part being run and the lower press member is activated to lift the sheet from the conveyor and press it against the stationary upper press member. The elevation at which the upper press member is set is determined by several factors including the stroke of the hydraulic cylinder of the lower platen and the curvature and thickness of the glass sheet being run. To properly position the upper press member, the lower press member first is raised to an elevation above the supporting surface of the conveyor. The jack system associated with the upper platen is then manipulated to position the shaping surface of the upper press member at a distance from the lower shaping surface representative of the thickness of glass sheet to be bent.
While the above-described apparatus has been successful for bending glass sheets to satisfy most present day requirements, the trend to aerodynamic styling in the automotive industry has resulted in glazing closures with more pronounced curvatures and complex shapes. The relatively deep curvatures of some of these closures are becoming increasingly more difficult and, in some instances, impossible to form on conventional bending apparatus.
On conventional apparatus, the glass sheets are generally formed to a concave curvature as viewed in elevation, and the degree of curvature has a determining effect as to the elevation or vertical position at which the sheets are pressed. The deeper the curvature of the sheet, the farther the lower press member is required to travel to lift the sheet from the conveyor to a position thereabove for pressing against the upper press member. Since the upper press member is fixed at this elevation, it must not be in a position to interfere with the glass sheets entering and leaving the press area. Due to the stroke limitation of the lower hydraulic cylinder and structural obstructions on the lower press member, it is oftentimes impossible when bending deeply curved sheets to establish the fixed position of the upper press member at an elevation that does not interfere with the travel of the glass sheet. The problem is further complicated when employing a shuttle carrier system for removing the curved sheet after bending. In this instance, a vacuum male mold is used to support the sheet after bending, and sufficient space must be provided between the conveyor and the supported sheet to permit entry of the carrier ring.
Of course, it is conceivable to utilize the existing upper screw jack system for maneuvering the platen frame in a reciprocating manner to alternately move the upper press member from a position that permits unobstructed conveyance of the glass sheet to the preselected position for pressing the glass sheet. While the system is capable of functioning properly in this manner on a production basis, the maneuvering of the entire platen frame assembly with the press member during each bending cycle would substantially reduce the speed of the operation, adversely affecting productivity.
While these problems are evident when bending automotive glazing closures having relatively deep curvatures as discussed above, they also are encountered when bending other deeply curved glass products such as architectural glazing and the heretofore mentioned glass satellite dish.